How Much Do We Really Know About Venus?

Venus used to be described as a sister planet because it shares a similar size, mass, and composition with Earth. But the similarities end there. Venus's 900-degree-Fahrenheit temperature, sulfuric acid atmosphere, and overwhelming air pressure (93 times greater than our home planet's) have ruled out manned missions, leaving scientists with the challenge to develop technology and techniques to withstand such a harsh environment.

For more than a half-century scientists have launched a barrage of complex equipment to the second planet from the sun, hoping that the instruments will survive the harsh Venusian climate long enough to transmit data. So far, the record to beat is 127 minutes. Orbiters have reached the second planet and tried to peer through its yellow haze, and last year scientists at NASA's John Glenn Research Center submitted a proposal for using landsailing technology to navigate the Venusian surface.

With increasing interest in exploring our closest planetary neighbor, here is a look at what's come before, including the Greeks, a Soviet obsession, and beyond.

Mariner

The earliest known mention of Venus is from the Babylonians, dating around 1600 BCE (they called it Nindaranna). The Greeks believed the planet to actually be two separate celestial bodies, Phosphorus and Hesperus. The mathematician Pythagoras discovered that the two were actually the one and the same. While European astronomers learned a few things about Venus in the 1600s and 1700s, the planet remained mysterious until humanity figured out a way to send probes there in the 20th century.

Until the space race of the 1950s and '60s sent the U.S. and Soviet Union clamoring for solar system supremacy, scientists didn't know what kind of atmosphere to expect on Venus. Considering its similarity to Earth, it was possible that Venus supported habitable conditions. However, radiometer experiments in the late 1950s unveiled a blistering planetary surface.

Nevertheless, Americans and Soviets rushed to send probes to Venus with the Mariner and Venera programs, respectively. Both endeavors ran into trouble as early iterations were plagued with launch and in-flight failures, but on Dec. 14, 1962, NASA's Mariner 2 successfully recorded temperature and atmospheric conditions on Venus. This marked the first successful encounter between a spacecraft and another planet.

The craft discovered that, unlike Earth, Venus was uniformly hot. They also found that Venus has an amazingly slow rotation, and that it actually spins in the reverse of Earth's. A Venusian day (243 Earth days) takes longer to complete than a Venusian year (224.7 Earth days).

Venera

Five years later, after a couple of failed launches due to overheating, the USSR successfully landed the Venera 4 probe on Venus, making it the first man-made object to land on another planet. The Venera program would go on to have 16 launches, with its final mission in the early 1980s.

If a Venera craft was lucky enough to reach the surface, it soon succumbed to the planet's immensely inhospitable environment, with temperatures hot enough to melt lead. The vessels recorded data for only an hour or two.

Vega

In the mid-'80s, the USSR began the Vega program, with some aspects similar to the earlier Venera spacecraft. However, this mission had two parts, as the vessels would also do a flyby of Halley's comet.

Each craft, Vega 1 and 2, contained a balloon explorer and lander. The balloons were designed to travel in the upper atmosphere where temperatures were much more tolerable. They traveled 7500 miles and transmitted for two days collecting data on the size and distribution of cloud particles. The Vega lander was able to measure the planet's otherworldly surface, finding anorthosite-troctolite rock, a chalky white rock not easily found on Earth but in great abundance on the moon's highlands.

Magellan

In 1990 the long-awaited Magellan spacecraft entered Venus's orbit and began fulfilling its primary objective: mapping the planet. The image resolution from Magellan was 10 times great than Venera missions 15 and 16. The orbiter was able to map 98 percent of Venus.

What Magellan saw was a planet almost entirely covered in volcanic flows. It spotted evidence of tectonic activity, turbulent surface winds, and multiple lava channels. In October 1994 the Magellan spacecraft performed one more maneuver—plunging into the Venusian atmosphere. NASA lost contact with the orbiter before it made impact, though scientists believed the probe reached the surface.

Venus and the World

Interest in Venus waned after the Magellan mission. The only new data came from flybys by orbiters destined for other planets, such as the Messenger probe that is now studying Mercury.

In 2005 the European Space Agency (ESA) broke the decades-long duopoly on Venus exploration held by the Cold War superpowers. Its spacecraft, named the Venus Express, entered orbit in April 2006 and continues to transmit back to Earth. The craft's objectives include discovering how the planet's cloud system works, how the greenhouse effect plays into the evolution of Venus, and what caused the global volcanic resurfacing of Venus 500 million years ago.

Japan also attempted to enter the Venus-exploration arena, launching the Akatsuki orbiter in 2010. Much like the "7 minutes of terror" that NASA's Curiosity team experienced as they waited to hear whether the rover had landed successfully on Mars, the Japan Aerospace Exploration Agency experienced a 3-minute blackout as their craft approached Venus. But on the other side of the silence came bad news: The orbiter failed to enter orbit with Venus, having not burned the engines long enough. The team will attempt to insert Akatsuki in Venusian orbit in 2015. The ESA hopes to conduct joint missions with the probe once it enters orbit.

The Indian Space Research Organisation announced plans last year for a Venus mission to study the atmosphere and answer lingering questions on the origin and evolution of planets. The Venera-D is the Russian Federal Space Agency's first probe to Venus, which will carry out missions similar to previous Venera probes and NASA's Magellan. The probe will carry a suite of devices, including an orbiter, a subsatellite, balloon probes, and a lander. The mission won't begin until at least 2024.

Going Sailing

An ambitious proposal from Geoffrey Landis at NASA's John Glenn Research Center is to develop a rover that works with Venus's topography and winds. Landis's landsailing rover, the Zephyr, has been discussed for more than a year, but broke into the news with a flurry of reports last month. Zephyr will be considerably less burdened by instruments than NASA's Curiosity rover but will still need a detailed landing procedure. The rover would be powered primarily by surface winds, and all-electric power would be used for radio and science equipment designed to withstand Venus's climate.

Landis hopes to sail the surface of Venus, visit unknown landforms, and find the closest answer to the age-old Venus question: What exactly is going on here?

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